Resistor color bands

The colored bands on resistors indicate their electrical value and tolerance, following an internationally standardized code since the 1920s.

About this subject

Resistors are passive electronic components that limit electric current flow. Their value in ohms is indicated by colored bands printed on the body, a system created by the Radio Manufacturers Association (RMA) in the 1920s and later adopted by the International Electrotechnical Commission (IEC). Each color represents a digit from 0 to 9, and the band sequence allows reading the nominal resistance.

The most common code uses four bands: the first two represent significant digits, the third is the multiplier (power of 10), and the fourth indicates tolerance (gold = ±5%, silver = ±10%, no band = ±20%). Precision resistors have five or six bands, with the third band serving as an additional significant digit. Black (0) is never used as the first band because leading zeros are not represented.

Standardized values follow series such as E12 (12 values per decade) and E24, facilitating mass production. The color code is universal, but correct reading requires orientation: bands are read from the end closest to the edge, with the tolerance band usually farther apart. Carbon-film and metal-film resistors, common in electronic devices, have used this system for decades.

Interesting fact: military and high-reliability resistors may include a fifth band for temperature coefficient (ppm/°C), indicating how the value changes with heat. Learning to decode the colors is a fundamental skill for technicians and hobbyists, preventing errors in assemblies and repairs.

Frequently Asked Questions

How to read a 4-band resistor?

Read from the end closest to the edge: first two bands are digits, third is multiplier (e.g., red = 100), fourth is tolerance (gold = 5%). Example: brown, black, red, gold = 10 × 100 = 1000 Ω (1 kΩ) with ±5%.

What is the color code sequence for resistors?

Black (0), brown (1), red (2), orange (3), yellow (4), green (5), blue (6), violet (7), gray (8), white (9). For multiplier: black = 1, brown = 10, red = 100, etc. Tolerance: gold = 5%, silver = 10%, none = 20%.

Why do some resistors have 5 or 6 bands?

Precision resistors use 5 bands: three digits, a multiplier, and a tolerance (usually 1% or 2%). The sixth band indicates temperature coefficient, showing how resistance changes with temperature in ppm/°C.